Add the milk, cream, condensed milk, chocolate chips, cocoa powder, and salt to the slow cooker insert. A 4-5 quart slow cooker works well.
Whisk until well-combined.
Cover, and cook on LOW for about 2 hours, or until the chocolate has melted, stirring every 30 minutes or so.
Turn the slow cooker to WARM.
The hot chocolate can stay on warm for about 2-3 hours.
Give it another good stir before serving.
Top with desired toppings just before serving.
Store leftover hot chocolate in the refrigerator for up to 5 days.
Notes
Milk - Feel free to use any milk from skim milk to whole milk.
Heavy cream - The hot chocolate is very rich! You can use milk in place of the heavy cream if you prefer.
Sweetened condensed milk - Be sure to use sweetened condensed milk and NOT evaporated milk as the sweetened condensed milk provides the sweetness for the hot cocoa.
Semisweet chocolate chips - You can use milk or bittersweet chocolate chips depending on how sweet you would like the cocoa to be.
Unsweetened cocoa powder - I use unsweetened cocoa powder, but Dutch-processed would also work.
Vanilla extract - You can omit the vanilla extract or use another extract, like peppermint, if you prefer.